Use of the EPIC model to predict runoff transport of surface-applied inorganic fertilizer and poultry manure constituents

The Erosion Productivity Impact Calculator (EPIC) model was applied to four fields established in 'tall' fescue (Festuca arundinacea Schreb.) in northwestern Arkansas to predict runoff and transport of nitrogen, phosphorus, and sediment. Fertilizer form varied among the fields with two receiving inorganic fertilizer, one receiving poultry (Gallus gallus domesticus) litter, and one receiving poultry manure. Soil and grazing parameters also differed among fields. Runoff and nutrient/sediment transport observed over 20 months were compared to EPIC predictions generated without calibration. Significant correlation between event predictions and observations were found in half the cases. There was significant correlation between observed and predicted calendar year total transport for all outputs except nitrate-nitrogen. The findings indicate that EPIC can accurately reflect runoff quality trends when executed without calibration for pasture fields in northwestern Arkansas

Nitrate-nitrogen losses to groundwater from rural and suburban land uses

Nitrate-nitrogen (nitrate-N) losses to groundwater from septic systems, forests, home lawns, and urea- and manure-fertilized silage corn were quantified and compared. The septic system and all silage corn treatments had annual flow-weighted concentrations of nitrate-N in excess of 10 mg/l for at least 1 of the 2 years. Forest and both fertilized and unfertilized home lawn treatments generated flow-weighted nitrate-N concentrations of less than 1.7 mg/l. Annual losses ranged from greater than 70 kg/ha of nitrate-N from silage corn treatments to less than 1.5 kg/ha from unfertilized home lawns and forest. The results demonstrate the importance of unfertilized land use types in maintaining aquifer water quality. Replacing production agriculture with unsewered residential development will not markedly reduce nitrate-N losses to groundwater. -from Author

Denitrification in grass and forest vegetated filter strips

Denitrification was measured in two grass and two forest vegetated filter strips (VFS) in Rhode Island. The grass plots were established on a well-drained soil and were planted to either tall fescue (Festuca arundinacea) or reed canarygrass (Phalaris arundinacea). One forest site was on an excessively well-drained soil and was dominated by oak (Quercus sp.), and the other was on a poorly drained soil and was dominated by red maple (Acer rubrum). Denitrification was measured using soil cores under aerobic and anaerobic conditions with a range of treatments: no amendment, actylene, water, nitrate (NO3-), NO3- plus C. Unamended rats of denitrification were low in all plots. Nitrate and NO3--plus-C amended rates were consistently higher in the grass plots than in the forest plots. Nitrate-plus carbon-amended rates were higher than NO3--amended rates in all plots, but the differences were significant (P \u3c 0.05) in the forest plots only. Denitrification enzyme activity (DEA) was measured in 14 additional forest sites of varying natural drainage classes and was related to soil moisture (r2 = 0.56, P \u3c 0.01) and pH (r2 = 0.43, P \u3c 0.01) at these sites. The results suggest that the ability of VFS to support denitrification varies strongly with vegetation, soil type and pH, and that denitrification in VFS may be amenable to management

Assessing Site Vulnerability to Phosphorus Loss in an Agricultural Watershed

A P index was developed as a tool to rank agricultural fields on the basis of P loss vulnerability, helping to target remedial P management options within watersheds. We evaluated two approaches, a soil P threshold and components of a P index, by comparing site vulnerability estimates derived from these two approaches with measured runoff P losses in an agricultural watershed in Pennsylvania. Rainfall–surface runoff simulations (70 mm h-1 for 30 min) were conducted on 57 sites representing the full range of soil P concentrations and management conditions found in the watershed. Each site was comprised of two, abutting 2-m2 runoff plots, serving as duplicate observations. For sites that had not received P additions for at least six months prior to the study, Mehlich-3 P concentration was strongly associated with dissolved P concentrations (r 2= 0.86) and losses (r 2=0.83) in surface runoff, as well as with total P concentration (r 2= 0.80) and loss (r 2 = 0.74). However, Mehlich-3 P alone was poorly correlated with runoff P from sites receiving manure within three weeks prior to rainfall. The P index effectively described 88 and 83% of the variability in dissolved P concentrations and losses from all sites in the watershed, and P index ratings exhibited strong associations with total P concentrations (r 2 = 0.81) and losses (r 2 = 0.79). When site-specific observations were extrapolated to all fields in the watershed, management recommendations derived from a P index approach were less restrictive than those derived from the soil P threshold approach, better reflecting the low P loads exported from the watershed